It is already known in the art to emboss sheets comprising multiple plies of creped tissue to increase the surface area of the sheets thereby enhancing their bulk and water holding capacity. Paper towels and toilet tissue are usually marketed in rolls containing a specified number of sheets per roll. Paper towels or tissue embossed in conventional patterns of spot embossments, when packaged in roll form, exhibit a tendency to be non-uniform in appearance due to the tendency for ridges to form on the roll along the lines of the bosses as the sheet is wound onto the roll.
Embossment patterns typical of conventional products have a tendency to cause nesting of some of the bosses and stacking of others when the embossed tissue rolled on a hollow core or mandrel. The so-called line patterns, e.g. the pattern illustrated in U.S. Pat. No. Des. 242,579 are especially prone to nesting of the bosses in the product roll whereas dissimilar patterns tend to pile up on top of one another. Since the appearance of a roll of toilet tissue or paper towels is an important attribute suggestive of quality of the product, as well as its softness and absorbency, it is most desirable to avoid resulting nonuniformity of rolls of product, especially those products sold to individual consumers in supermarkets.
It has been proposed heretofore to emboss paper products to avoid nesting of the bosses in rolled, folded, or stacked sheets of paper products by various means including embossing the sheet with bosses of varying configurations, e.g. as in U.S. No. Des. 230,311 or alternating sheets or strips embossed with one pattern with sheets or strips embossed with another pattern, or alternating embossing patterns on a single strip, e.g. U.S. Nos. 1,863,973; 2,177,490; and 2,284,663.
Such fibrous sheet products, generally termed non-woven fibrous webs, when produced on a paper making machine are non-uniform in tensile strength, having a greater tensile strength in the machine direction than in the cross-machine direction. When rolled, a strip of the sheet material is wound onto a mandrel or hollow core in the machine direction with perforations in the cross-machine direction to facilitate tearing off sheets from the strip. Conventionally, rolls of paper toweling and toilet tissue are perforated to produce an approximately square sheet when separated into individual sheets at the perforations.
When the sheets or webs are embossed, the embossment most frequently comprises repetitive parallel rows of identical or alternating boss patterns arranged in the cross-machine direction perpendicular to the machine direction. The boss patterns are also in alignment with one another in the machine direction, with identical bosses appearing either in adjacent cross-machine rows or in alternate rows once or twice removed. Alignment of bosses in the machine direction frequently causes "ridging" of the roll product detracting from its appearance. While alternating the patterns of individual bosses reduces the nesting of the bosses in the finished roll products, the expense of the machine embossing roll necessary to produce such patterns of embossment is considerably increased. This invention provides a solution to the above-mentioned problems by providing a method of embossing with identical bosses while avoiding both ridging and nesting of bosses in the rolled product.
By the method of embossment disclosed in U.S. Pat. No. 4,659,608, incorporated herein by reference, it is possible to produce paper toweling and toilet tissue and rolls of product produced therefrom by embossing a pattern of uniformly spaced identical bosses in angular rows on a continuous sheet or strip of non-woven fibrous webs of the towel and tissue type. Embossing in this manner enhances the absorbency and softness of the sheet and results in a spiral wound roll package of improved uniformity and appearance.
The method disclosed herein of embossing such fibrous web products avoids many of the problems associated with prior art methods and the products so produced. In one specific preferred embodiment of this invention, the method of embossing fibrous webs disclosed in my issued U.S. Pat. No. 4,659,608 is combined with the method disclosed herein to produce a multi-ply tissue of enhanced bulk, softness and absorbency.